Culinary herbs together with aromatic plants such as ginger, garlic, peppers and chillies, are much prized ingredients in cooking. Fresh herbs are cultivated in home and commercial gardens and today are available fresh in many varieties. Herbs are used in the preparation of numerous traditional dishes and the aroma and color of various specific herbs are of great importance in these.
In most parts of the world, fresh herbs are seasonal. Herbs may be obtained year round in dried form. Most herbs when dried, however, lose their green color, aroma and flavor and are irreversibly altered so that they do not represent a satisfactory alternative to freshly picked herbs.
Many of the popularly used herbs contain enzymes which act very rapidly when the cell structure of the herb is disturbed resulting in loss of green color, production of dark pigments and both loss of fresh flavor and the development of off-flavors. These changes occur more rapidly at elevated temperatures such as occur in many food processing operations and in cooking. Amongst these herbs are basil, coriander (cilantro), oregano, tarragon and mint. Many studies have been made on the enzymic degradation of herbs including those by Baritaux et al., (Sciences-des-aliments 1911, 11, (1)49-62), Gerherdt, V. et al. (Fleischerei 34(5)508-208). Studies have also been made on the drying and storage stability of dried herbs, including those by Mastrocola, D. et al. (Industrie-Alimentari, 1988 27(259(341) and Paeaekkoenen, K., et al. (J Food Science 1990, 55(5)1373-1377).
Many herbs can be obtained nowadays in frozen and freeze-dried form. Frozen herbs have good flavor and color, but must be kept frozen and when thawed or used in cooking and in processed products are subject to the same enzymic action and color and flavor changes as fresh herbs. Freeze-dried herbs, which are expensive to produce, when wetted, suffer from the same enzyme action as frozen herbs.
The enzyme action in herbs can be prevented by blanching of the herbs in steam or hot water. In this way, the green color can be largely preserved but the flavor is often almost completely destroyed. Ricci in British Patent No. 1,348,266 (1974) describes production of a green food flavoring by heating basil leaves in hot water, quenching in cold water, cutting into pieces and refrigerating.
Herbs, along with other vegetables, for many ages have been traditionally preserved by pickling with salt or salt brine with or without vinegar. This method is used extensively in the pickle industry. Herbs treated in this way lose their attractive bright green color and much of the flavor is lost into the brine. Unless pasteurized these products are subject to surface molds and to salt and sugar tolerant yeasts. Coste (British patent 2,014,429, 1979) claims to have preserved chopped herbs by mixing with water activity controlling substances such as salt, glycerol and propylene glycol in such concentration that the water activity is less than 0.90. Oil up to 20% may be added to give a pasty consistency. We have observed that in following the procedures described by Coste, the resultant herb mixes developed quickly a dark olive green color. In the case of the herbs with high levels of polyphenol oxidase enzymes such as basil, mint and oregano the color that developed on storage was a dark greenish black. In all cases, the color changes were accompanied by off-flavors. Moreover, it was observed that even at water activities of 0.80, yeast and mold growth could occur on the surface of the mixes.